Beam Instrumentation

The goal of the VI Working Group 2 is to reveal properties of accelerated electron bunches at FLASHForward by developing appropriate diagnostics. This includes planning, development, building, installation and operating the diagnostics as well as interpreting and publishing the results. The parameters of plasma-accelerated beams differ from those in conventional accelerators, therefore the existing methods need to be adapted and/or the new ones have to be developed.
Projects currently pursued in the group include design of the post-plasma electron beamline (optics, standard diagnostics), energy and emittance measurement, longitudinal diagnostics with transition radiation and Smith-Purcell radiation, X-ray diagnostics etc. The group is a collaboration between the FLA group at DESY, John Adams Institute (UK), Imperial College London (UK). Colleagues from the SPARC-Lab at the INFN (Italy) are also involved.

As an example, the figure shows the layout of the post-plasma beamline for FLASHForward as designed by the Working Group 2.
The initial section (beam capturing) consists of several quadrupole magnets focusing the divergent witness beam.
After the quadrupoles, a dipole magnet is located, acting as a broadband energy spectrometer.
Several meters of drift space following the dipole are needed so that the witness beam size reduction takes place.
At the point where the beam is sufficiently small, a collimator is located;
it rejects the drive beam while the witness passes through unaffected.
The emittance measurement section consists of another quadrupole magnet and a profiling screen.
Finally, a high resolution spectrometer determines precisely the energy distribution of the witness beam.
Various diagnostics will be located along the beamline, such as the longitudinal profile measurement using transition radiation or diagnostics of the ionisation laser.
After passing through, the beam may be manipulated further to demonstrate lasing in the undulator.

Point of contact

Dr. Ivan Konoplev (JAI) and Dr. Vladyslav Libov (DESY)